Abstract - Propionibacteria are cheese starters, also studied for their probiotic potential. An interesting feature is the ability of some strains to synthesize nitric oxide (NO) from nitrate reduction. NO production is hypothesized to be the mechanism by which some probiotics improve the mucosal barrier in rats. We therefore investigated the ability of two Propionibacterium acidipropionici strains (TL15 & TL223), which differ in their in vitro production of NO, to improve colitis in rats. Three groups of rats in which colitis was induced by trinitrobenzene sulfonic acid (TNBS), received intracolonic infusions of 9 g·L-1 NaCl (n = 6), or 0.9 × 1010 CFU·d-1 of TL15 (n = 7), or 1.4 × 1010 CFU·d-1 of TL223 (n = 7), for 7 days. Following treatment, animal weight, food consumption, inflammatory score and myeloperoxydase (MPO) activity, together with changes in intestinal bacteria and SCFA concentrations, were investigated. As expected, both TL223 and TL15 supplements induced detectable counts of P. acidipropionici in colonic contents of rats (7.67 ± 0.67 and 7.43 ± 0.50 log eq. CFU·g-1, respectively, as determined by real-time PCR). Food consumption and body weight of rats receiving propionibacteria were overall higher than those of rats with NaCl (P = 0.007 and P = 0.004). Moreover, both propionibacteria infusions similarly and dramatically reduced the gross score for inflammation (P = 0.004) as compared with NaCl (0.6 ± 0.3 and 0.7 ± 0.5 vs. 4.8 ± 1.5). A similar effect was observed for MPO activity (P = 0.056), which reached 2.50 ± 1.37 U·g-1 of mucosal tissue for NaCl vs. 0.05 ± 0.02 and 0.26 ± 0.18 U·g-1 for TL223 and TL15, respectively. This study shows for the first time the potential benefit of propionibacteria in colonic mucosa healing, but the mechanism involved needs to be elucidated.